Just stripped my newly acquired 198B prior to a total rebuild, having experience of a 199A only. The 198B is fitted with a tiny flywheel compared to the 199A, so I am wondering if this is correct or if it might benefit from a bigger one. The torque and power of the 199A makes it a pleasure to ride, but I am worried that a tiny flywheel on the 198B might make the engine too lively and revvy, Is it the correct flywheel and if so, will it be more like riding a modern bike than the 350 motor, with its bags of torque? Any suggestions gratefully accepted.

From what I've seen of them and from what is fitted to my own, that seems to be the usual size flywheel that was fitted to the 198b

As for what it does to the engine, I haven't finished rebuilding mine yet so never ridden it, but you need to ride it for yourself as everyone's perception of good/bad is different. Easy enough to fit the bigger weight normally fitted to the 250 if you don't like it though.

Thanks Woody, I'll certainly try it and report back. I have just noticed that you and Smelling123 (Stu?) had a debate about this on TC in April 2012 and he was going to try his 198B after a rebuild, which seems to be exactly the same, but I can't find his eventual opinion of it anywhere on the site. (Light flywheel, single row primary chain)

I may be panicing a bit, but the weight struck me as really minimalist in comparison with the 350, especially as it is coupled to an aluminium clutch cage. Mind you, the existing Femsa ignition flywheel is a bit of a beast, so perhaps that is sufficient to keep the engine from stalling so easily. Not to worry, it ain't going to turn me into another Raga whatever effect it has on the engine!

As you suggest, it is easy to change if necessary.

I don't think you need to worry about it. I finally got around to having a proper ride on my 198b at a Sidcup practice trial last week. I recently finished a mostly cosmetic rebuild my brother started many years ago (prompted by me bending the gear shaft in a trial about 20 years ago) and the bike is bog stock and low mileage. I was even considering selling it but, having ridden it, changed my mind. I've not ridden a 350 so can only say that the 250 'plonks' along well, has good pick up, grips really well and revs out well - everything you want from a trials engine infact. I reckon you're going to love it!

There are generally two clutch / crank flywheels on the Sherpa engines, a big thick single weight on the 250 and a bigger double weight on the 325/340.

The smaller and thinner single weight fitted to the 198b may be offset on the ignition side by using the heavier ignition flywheel usually found on the 325/340. When they built the 198b they were probably scraping the bottom of the parts bins and using whatever was left.

I also have a '76 325 motor which has a small weight like the 198b but it uses a double row primary chain and clutch basket. I think the thin single weight originates from the Pursang.

As Mr Pigbog says, they ride very nicely with this flywheel... the 250 has quite soft power delivery compared with the bigger engines anyway... I luv how they run!

Hi bige

Yes mine has the small flywheel likes yours. I love the motor, it's nice and soft but goes when you need I'm from a road racing background so I'm not keen on engines that feel flat.

I'd leave yours as it is and try it - very easy to fit a bigger one in the future.

Cheers

Stu

Leave well alone, the flywheel you show is the correct one and bike will run fine

Only flywheel worth messing with is the one fitted to the 175cc which were lazy to say the least, and I used to turn these down on lathe to try to liven them up, but even that was a bit of a ase of time

Usually in such matters Mr Bult got it pretty close, and you will not need to worry about riding it as it will be spot on

Thanks for all the advice fellas, it may be a month or two off yet but I am looking forward to trying it. I'll stick to what I've got for the time being and let you know how it goes. From what I have found so far, the engine has had a fairly hard life, made even worse by someone's previous attempt at a rebuild using blacksmith's tools only! It's surprising what damage a tame monkey can do with a Manchester spanner.

In the meantime I'll stick to the 350, it's a pleasure to ride.

Funnily enough, it was Mick Bowers who suggested I try a 250, he reckons they are better in all respects than the 350, and who am I to argue with him?

Thanks again and cheers,

Chris.

like this 1

some more photos off the 198B